1. Field of the Invention
The present invention relates to a process for manufacturing free-flowing metal foam with monomodal distribution of the dimension of the cavities in said foam. More precisely, the invention deals with the preparation of metal foams each with essentially the same pore volumes for use in molded articles with a specific profile of properties. The invention also relates to a device for producing a metal foam. Finally, the invention relates to the use of components which contain a largely homogeneous foam formation.
2. Discussion of Background Information
Metal foam, particularly lightweight metal foam, is being used to an increasing degree in molded articles with a special spectrum of properties, whereby the various requirements must be met with a high degree of certainty. In other words, the molded articles with low weight are supposed to feature high stability with precisely specified mechanical stress and/or be deformable with maximum energy absorption in the case of overload.
Fabricating objects of metal foam is known. For example, a process for manufacturing a foamed article is described in WO 01/62416 A1, according to which an ingot mold is filled with foam by collecting individual bubbles rising in the melt. However, this process, in which the gas bubbles are introduced and isolated for the most part by way of a so-called rotor impeller, has the disadvantages that, on the one hand, filling the ingot mold is slow and, therefore, with a cooled ingot mold wall, the part of the article that was formed last has a frequently disadvantageously thick wall layer, and, on the other hand, the bubble size is embodied variably in an uncontrolled manner. As a result, the mechanical characteristic values of a part or article created in this manner often feature a great dispersion that is unfavorable for the most part.
Another process has become known from EP 0666784 B1, in which a molded casting of the stabilized, fluid foam metal takes place by pressing the stabilized foam into a mold with pressure. However, the cells of the formed foam cannot be produced in a uniform size with this process.
Austrian patent application 936/2001 discloses a device and process for introducing gas into molten metal, whereby a uniformity of the diameter of the respective individual bubbles and the size of the gas bubbles are controlled.
A monomodal distribution of the dimension of the cavities of a molded article made of metal foam as well as a process for manufacturing the same is disclosed by Austrian patent application 935/2001.
However, all the manufacturing methods that can be attributed to the state of the art for free-flowing metal foam share the disadvantage that individual bubbles do not usually connect until they are brought together and often form thickened wedge areas. In addition, it is possible that a desired filling speed of a mold for the purpose of obtaining a uniformly thick surface layer of the article or a preferred metal flow cannot be achieved.
For the most part, the known devices do not permit coherent metal foam bubbles of the same size to be manufactured in such a way that the interstructures between the cavities can be embodied to be thin and perform favorable support functions with regard to a low specific weight with high mechanical characteristic values of the part.